The present invention relates to an apparatus for diagnosing an air bag equipment, and more particularly to an apparatus for the diagnosis apparatus in which a central processing unit (designated as a CPU hereinafter) provided therein includes a timer circuit.
There have been proposed many kinds of air bag equipment for safety, which are mounted in front of a driver and passengers in a motor vehicle. The air bag equipment is a safety equipment which is capable of protecting persons from impact forces when the vehicle collides, in the manner that an ignition of an squib causes high pressure gas to momentarily expand and fill the bag in front of the persons so that the inflated air bags protect them.
FIGS. 1A to 1E show one example of the air bag equipment. An air bag equipment 50 comprises, as shown in FIGS. 1A and 1B, an air bag 51 provided in a vicinity of a steering mechanism in the vehicle. An inflater 52 is attached to the air bag 51 and generates an inert gas such as a nitrogenous gas when the vehicle is subjected to impact forces due to a collision. A pair of compartment sensors 53 and 54 are provided on both front sides of the vehicle and detect strong impact forces of approximately 12G from front direction to expand the air bag 51. A diagnosis control unit 55 and the compartment sensors 53 and 54 are connected by wirings 56 and 57 provided in the vehicle. The unit 55 is connected to the inflater 52 by a wiring 58 to output a gas generate command. The control unit 55 provides a signal to actuate the inflater 52 by strong impact force of approximately 2G from the front direction.
The compartment sensors 53 and 54 described above, as shown in FIGS. 1C and 1D, are provided in cases (not shown) filled with inert gas. A main body 60 of the sensor 53 or 54 comprises a switch 61 provided on a base, a rolled plate spring 62 which has a notch 62a causing the switch 61 to be exposed. Both ends of the plate are fixed to the base, and a center portion of the plate is rolled around a roller 63. The main body 60 operates in the manner that the roller 63 rotates in the direction indicated by the arrow R in FIG. 1D to make the switch 61 turn on when the vehicle receives a strong impact force S from the front direction.
The sensors 53 and 54 mentioned above, as shown in FIG. 1E, are connected in the manner that a heater 52A of the inflater 52 is connected to both of the compartment sensors 53 and 54 and switches 55A and 55B in the diagnosis control unit 55. And the sensors 53 and 54 are connected a negative electrode of a battery 59, and the switches 55A and 55B are connected to a positive electrode of the battery 59.
The air bag equipment has sensors for detecting collision impact forces or the like, a squib to expand the air bag must have high reliability without the occurrence of fault or failure.
That is, in the case that the air bag is not inflated during a collision because of the occurrence of faults while in operation, it is impossible to sufficiently protect the persons in the vehicle, thereby causing problems of safety. Furthermore, reliability of the air bag equipment is reduced if the air bag would be expanded by faulty operation while the vehicle is running and the expansion of the air bag obstructs the sight of the driver.
Accordingly, there is proposed a diagnosis apparatus for diagnosing faults in air bag equipment in order to prevent occurrence of faulty operation for the purpose of ensuring reliability of the air bag equipment. There is disclosed "FAULT DIAGNOSIS CIRCUIT FOR AIR BAG EQUIPMENT", as a typical example of conventional diagnosis apparatus, which is published in the Japanese official gazette of Patent publication No. 55-45414 (1980).
In the prior art, a diagnosis apparatus for faults of air bag equipment is provided in the diagnosis control unit 55 as shown in FIG. 1A. A diagnosis apparatus 1 comprises, as shown in FIG. 2, a sensor 2 for detecting whether or not the air bag 51 is operated in a normal condition, a fault detection circuit 3 for detecting faults occurring in the sensor 2 and outputting a fault detection signal, a central processing unit (designated as a CPU hereinafter) 4 which receives the fault detection signal detected by a fault detection circuit 3 and determines a fault condition, a fault occurrence position and time registered by a built-in clock, and a memory device 5 for successively storing the fault condition, the fault occurrence position and the time as calculated results of CPU 4.
The diagnosis apparatus 1 is driven by direct current (DC) electric power supplied from a power apparatus 6 which comprises a battery 11 mounted on the vehicle in order to drive the diagnosis apparatus 1. The conventional power apparatus 6, which is applied in the diagnosis apparatus 1 for the air bag equipment, is substantially comprised of only the battery 11, but has no control unit.
The diagnosis apparatus 1 mentioned above, however, has a problem of the battery 11 charge decreasing in the case where much time has elapsed from shipping until the first starting of the engine, and the diagnosis apparatus 1 has operated since shipping because the apparatus 1 has been connected to the loaded battery 11 before the shipping of the vehicle.
Furthermore, if the apparatus 1 is disconnected from the battery 11 between manufacturing and shipping in order to prevent the consumption of the battery 11, there are problems in that dealers may be reluctant to connect the apparatus 1 with the battery 11, and that the reliability of the entire system will deteriorate.